Modelling the seismic reflection characteristics in stressed layered media using reflectivity method

SUMMARY Initial stress exerts a crucial impact on the elastic properties and thus the wave reflection in the layered media. However, the stress effect on wave reflection characteristics in such media remain insufficiently understood. To address this issue, we develop a composite matrix reflectivity method incorporating initial overburden stress (CMRMS) by means of acoustoelasticity theory, enabling accurate modeling of seismic wave propagation in stressed layered media. The proposed method can better simulate multiple reflections, converted waves and transmission loss of seismic waves in layered media, compared to the classic stress-dependent reflection coefficient equation for a single interface. Moreover, our method can degenerate into the existing methods in the cases of no initial stress and single interface, which verifies its correctness. We further extended the CMRMS to elastic and viscoelastic non-welded interfaces using the linear-slip theory and standard linear solid model, respectively. The extended method is used to investigate the impacts of non-welded interface compliance, overburden stress, fluid viscosity and frequency on seismic reflection characteristics within layered model. It is shown that the stress effect magnitude on interface reflection significantly depends on the interface depth, due to cumulative transmission losses from overlying layers. Moreover, increasing either the compliance or the number of overlying non-welded interface significantly reduces the reflection amplitude at deeper interface. Our results show the potential of the proposed composite matrix reflectivity method to consider the joint effects of initial stress, multiple waves and transmission loss in both forward modelling and inverse applications.